The present invention relates to an engine control system for changing the acceleration response characteristics of a vehicle engine and method for controlling the same.
It is ideal if an automobile can be quickly and smoothly accelerated with increase in the amount of actuation of the accelerator pedal by the operator.
However, the drive-line system between the engine torque output shaft and the tires in an actual automobile is not considered as a complete by rigid body. In other words, the engine output cannot be instantaneously transmitted to the tires without being changed in the course thereof. The drive-line system includes components such as a main drive shaft, an axle shaft, engine mounts and suspensions. These components have elasticity which is a factor of a delay caused in the, drive-line system.
Accordingly, even if the engine torque output is increased to effect acceleration of the vehicle, drive-line system first absorbs the output energy the and then it releases most of the absorbed energy to the transmit it to tires after a delay of a given period of time. Simultaneously with this, a part of the released energy is reflected back to the engine. Tires are also elastic bodies, resulting in a delay until the transmitted driving force will become a propelling force relative to the road surface. Therefore, a part of the energy, of the driving force is reflected by the tires and is transmitted back to the engine.
Delay and reflection of the energy transmission in the drive-line system is vibrational. Reflection functions as braking for engine torque output to cause a change in the engine speed. If vibrational braking occurs in the engine and the drive-line system, a surging phenomenon could occur during a period of the acceleration. Since it is deemed that the surging phenomenon mainly depends upon the elasticity of the drive-line system, the surging phenomenon would be vibrational if the period of the vibration is close to a natural period of the vibration of the drive-line system. This will cause unwanted vibration rocking the vehicle mainly in a longitudinal direction, which makes the driver or passengers feel very uncomfortable. This may occasionally cause rolling and/or pitching of the vehicle.
In a vehicle, such a surging phenomenon during acceleration should be prevented from occurring. If such surging during acceleration is prevented from occurring and, simultaneously with this, the acceleration response characteristics of the vehicle can be preset to that which a driver desires, an appropriate driving characteristic can be attained depending upon the road surface and/or traffic conditions.
For example, since normally, there is very little opportunity for rapid acceleration during long distance driving on a less crowded free-way, the acceleration response characteristics represented by a relatively slowly increasing curve would be desired during this type of driving from the view point of comfort and fuel economy. On the other hand, a sharp acceleration characteristic may be necessary on streets in downtown where stop-and-go driving is frequent or on mountain roads. Alternatively, an acceleration characteristic intermediate therebetween may be necessary under other circumstances.
A method of controlling an engine to obtain an acceleration characteristic exactly reflecting a driver's intention is disclosed in Japanese Unexamined Patent Publication No. JP-A-60-175742 filed on Feb. 23, 1984 by Toyota Motor Company Ltd. The invention disclosed in this publication relates to a torque servo control, in which a target torque is calculated by a torque generation function with measured parameters, such as the extent of depression amount of the accelerator pedal and engine speed, so as to control an intake air amount and a fuel injection amount in such a manner that the output torque will become equal to a target torque according to a difference between the output torque actually measured by a torque sensor and the target torque.
Japanese Unexamined Patent Publication No. JP-A-59-113269 filed on Nov. 8, 1983 by Robert Bosh GmbH claiming Convention Priority based on German Patent Application No. P3243235.6 filed on Nov. 23, 1983 discloses a method of controlling vibrations, in which a vibration of an engine is detected and the polarity (positive or negative) of an ignition timing correction value is changed depending upon the vibration direction.
Japanese Unexamined Patent Publication No. JP-A-59-165865 filed on Mar. 9, 1983 by Toyota Motor Company Ltd. discloses a method of suppressing acceleration surging by controlling the ignition timing using a sinusoidal function signal having a frequency equal to a resonance frequency of a drive-line system and having a phase opposite to the phase thereof.
Although a torque servo system requires a torque sensor, it is difficult to realize a practical torque sensor which can perform an accurate torque detection in view of technical difficulty and cost. The torque servo has a long time lag until change in accelerator is converted into change in output torque so that it is difficult to accurately suppress the vibration by a feedback of the measured torque value.
A system for controlling ignition timing in response to detection of vibration of an engine is ineffective for an initial large vibration, since the vibration suppression action can be initiated only after the vibration occurs.
A system for controlling ignition timing using a signal having a frequency equal to and a phase, opposite to a resonance wave of a drive-line system has been proposed to detect an acceleration from a change in intake air amount per one rotation of the engine and to provide an ignition timing signal with a vibration control signal simultaneously with the detection of acceleration. In this case, there is a time lag from an initiation of acceleration action to torque generation via mixture intake, compression and expansion strokes. Accordingly, in this technique, there may occur a timing lag between commencement of longitudinal vibration of the vehicle due to initial torsional vibration and control. Therefore, there is a problem that not only cannot he above mentioned torsional vibration be timely suppressed, but also the vibration may be adversely amplified by a starting timing for correcting the ignition timing in the worst case.